Typical cellular communication systems include base transceiver stations (BTSs) that engage in wireless communication with mobile devices such as cellular phones. An example of such a system is illustrated in FIG. 1. The BTSs 14 of the illustrated system connect to at least one base station controller (BSC) 20 through a local network 16, and transmit and receive phone calls and other data using circuit-switched, time division multiplexed communications protocols, virtual circuit, asynchronous transfer mode (ATM) protocols, and/or other communications protocols. The term “local network” as used herein refers to a network served by a particular BSC 20. The local network 16 is typically an Internet protocol (IP) network, and can generally be considered part of a wider communication network having other portions which can include, for example, other local cellular networks and/or other types of networks such as the Internet. The other network portions can be referred to, with respect to the local network 16, as “outside” network portions. The local network 16 communicates to the outside network portions through a gateway 18.
FIG. 2 illustrates an example of a gateway 18 for use in the cellular communication system of FIG. 1. The gateway 18 includes an interface 40 for communicating with outside network portions, an interface 42 for communicating with the local network 16, a processor 44, and a data storage device 46 which stores information for use by the other components of the gateway 18. The stored information can include, for example, programs for execution by the processor 44.
A mobile device—a/k/a a “mobile unit” (MU) 12—engages in direct wireless communication with one or more of the BTSs 14 in order to ultimately communicate with another end-user device such as another MU or a hard-wired telephone (a/k/a a “land line”). The other end-user device can be within the geographic region served by the local network or can be elsewhere in the wider network—e.g., in an outside network portion.
A typical cellular network—which can include one or more local networks—covers a contiguous area that is divided into multiple cells. Each cell is served by a BTS 14 which provides a wireless link for at least one MU (e.g., a cellular phone) within the cell. The wireless link—which in many systems operates within the radio-frequency (RF) spectrum—is used to transmit electromagnetic data signals representing data being sent between the MU 12 and the BTS 14.
Consider an MU 12 which is engaged in a communication session (e.g., a telephone call). As the MU 12 moves among the cells, the session (i.e., the call) is handed off among the BTSs 14 in order to provide continuous coverage.
Typically, a BSC 20 controls call set-up within the BTSs 14, and inter-cell operations such as handoffs among the BTSs 14. In addition, the BSC 20 in conventional systems generally collects information about the respective BTSs 14 and controls the wireless communication parameters of the BTSs 14, such as transmission strength and modulation parameters. During call handoff, a local handoff controller 806 is used to control the allocation of resources among the other devices—e.g., the BSC 20 and the BTSs 14—which are connected to the local network 16.
For “uplink” communications—i.e., communications sent from a cellular phone or other MU 12—it is common to utilize multiple BTSs 14 to receive data from the MU 12. In conventional systems, the best-quality data signals from one or more of the BTSs 14 are selected by the BSC 20 in order to improve the quality of reception, as is well-known in the art. Typically, the stream of data transmitted from the MU 12 is broken into “frames” (i.e., portions of selected size).
For “downlink” communications—i.e., communications sent from one or more BTSs 14 to the MU 12—multiple BTSs 14 can send signals to a single MU 12 in order to improve the quality of reception, as is well-known in the art.
The above-described functions of: (1) selecting uplink signals received by multiple BTSs 14, and (2) distributing downlink signals through multiple BTSs 14 to a single MU 12, are typically performed by a software and/or hardware system called a “selection and distribution unit” (SDU). The SDU controls various characteristics of the digital transmission of the data to and from each MU. Such characteristics typically include parameters such as frame size and allocation of digital capacity such as bit transmission and processing capacity. In conventional systems, the SDU function is performed by the BSC 20. In addition, the allocation of wireless resources (e.g., wireless bandwidth) to an MU is also performed by the BSC 20. In particular, the BSC 20 also includes a wireless resource allocation function which assigns wireless bandwidth, spreading codes (e.g., Walsh codes), and/or time slots to the respective MUs connected to the local network 16. Moreover, digital transmission parameters such as digital capacity allocation are related to the quantity of wireless resources being used. For example, the digital capacity and the wireless capacity allocated to a particular MU must together increase with increasing data transmission rate. The BSC typically coordinates the SDU function and the wireless resource allocation function such that the allocation of wireless resources matches the allocation of digital resources.
The system of the claimed invention improves the capacity and/or coverage of a wireless communication system (e.g., Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), or Wideband Code Division Multiple Access (W-CDMA)) by reducing the required transmit power of the MU in simultaneous communications with multiple BSTs.